A charge-mosaic membrane is a membrane which consists of parallel arrays of anion-exchange and cation-exchange elements passing through the membrane. When the membrane is applied to the permeation of an electrolytic solution, circulating electric currents are passed between the anion-exchange and cation-exchange elements through which ions are passed. As a result, the electrolytes are rapidly transferred in comparison with the nonelectrolytes. This phenomenan can be applied for many usages. For example, the charge-mosaic membrane is applicable to a membrane of piezodialysis used for concentration of an electrolyte solution, although the concentration was difficult in a conventional membrane separation technique. It also is used as a dialysis membrane for separation of electrolytes from mixed aqueous solutions of electrolytes and nonelectrolytes, or for separation or purification of amphoteric electrolytes, such as amino acid.
The charge-mosaic membrane was initially prepared by a method wherein cation exchangers were united to anion exchangers or by a method wherein a resin membrane was partially immersed in a reaction solution for introducing both type of ion exchange groups into it (see U.S. Pat. No. 2,987,472; F. de Korosy, Nature, 197,635 (1963)). It is also reported that a membrane prepared by embedding a cation resin and an anion resin in a silicone resin membrane exhibits transfer phenomenon characterized by a charge-mosaic membrane (see J. N. Weinstein et al., Desalination, 12, 1(1973)). However, these initially developed membrane has large domains and are insufficient in mechanical strength. They also are difficult to produce in industrial scale.
Thereafter, it is also proposed that a charge-mosaic membrane is prepared by a casting method (see J. Shorr et al., Desalination, 14, 11(1974)), a blending method (Japanese Laid-Open Specification No. 14389/1979), a pile method or a suspension method. The casting method is a method wherein two different resins are poured in a mold and the blending method employs phase separation phenomenon which occurs when more than two different polymers are blended. The pile method is carried out by alternately piling a cation exchange film and an anion exchange film and then cutting it perpendicular to a film surface. Also, the suspension method is conducted by suspending particles having one ion exchange group in a polymer solution which can have the other ion exchange group to obtain a mosaic structure. These methods, however, have defects in formation of ion complex or film strength and therefore it is desired to obtain a charge-mosaic membrane not having the defects.
Nowadays, new methods, such as an ionotropic-gel membrane method (H. J. Purz, J. Polym. Sci., Part C, 38, 405(1972)), a latex-polymer electrolyte method (Japanese Laid-Open Specification No. 18482/1978) and a block copolymerization method (Y. Isono et al., Macromolecules, 16, 1(1983)), have been proposed. The ionotropic-gel membrane method is a method producing a charge mosaic membrane by forming an ionotropic-gel membrane having a columner pore of which gel portion was constituted with one ion exchange resin and then filling the pore with the other ion exchange resin. This method could realize an almost ideal mosaic structure if it was perfectly conducted, but actually such an ideal mosaic structure has not been obtained. The latex-polymer electrolyte method is divided into two. One is a method wherein a mixture of a styrenebutadiene copolymer latex and polystyrene sulfonic acid is formed into a film which is then cross-linked and chloromethylized followed by amination. The other is a method wherein a mixture of a styrene-butadiene copolymer latex and a quaternary aminated chloromethylstyrene is formed into a film and then cross-linked and sulfonated. It, however, is difficult for the above mentioned methods to control such chemical treatments. The block copolymerization method can miniaturize the size of ion exchange areas. In this method, the mosaic structure is obtained by utilizing microphase separation phenomenon when forming a film by evaporating a block copolymer solution. Then, anion and cation exchange groups are selectively introduced into the copolymer by suitable reactions to form a charge mosaic membrane. The method initially employed a diblock copolymer, but nowadays employs a pentablock copolymer. However, it is very difficult that each ion-exchange element passes through the membrane. It also is difficult to synthesize the block copolymers and to establish a film-forming process.
In the meanwhile, since it was found that a doped polyacetylene indicates metal conductivity, new conductive polymers has been intensely developed as well as the study of the electroconductivity of the polyacetylene. Especially, since a film of an aromatic compound was obtained by an electrolytic oxidative polymerization, development has been rapidly progressed.
A conductive polymer, such as polypyrrole, has electrochemical anode doping characteristics and therefore the anion of supporting electrolytes is grapsed by the positive charge of the partially oxidated matrix. In other words, as the oxidation potential of the polymer is lower than that of the monomer, the polymer prepared by oxidative polymerization is partially oxidized prior to the monomer. The polymer catches a counter anion of the supporting electrolyte in the electrolyte solution and thus anode doping is simultaneously progressed with the polymerization. This polymerization system makes it possible to enhance the electroconductivity of the polymer (for example, A. F. Diaz et al., J. Chem. Soc., Chem. Commun., 1979, 635; Japanese Laid-Open Specification No. 133127/1982; Japanese Laid-Open No. 226020/1984; M. Satoh et al., J. Chem. Soc., Chem., Commun., 1985, 1629).
Further, it has been reported that a conductive polymer easily prepared by electrolytic oxidative polymerization of a heterocyclic compound and aromatic amino compound has high conductivity and heat and chemical stability. This polymer, therefore, becomes noteworthy in wide variety of fields, such as organic secondary cells, sensors, optoelectronics, external control transfer membranes, organic electronics device, redox catalysts and the like, as well as organic conductive materials. However, it has not applied to a conjugated polymer-cation exchanger composite membrane yet.